1. Field of the Invention
The present invention relates to a compound semiconductor device and a method of manufacturing the same and, more particularly, a compound semiconductor device having a capacitor formed on a compound semiconductor layer and a method of manufacturing the same.
2. Description of the Prior Art
As the compound semiconductor device, the monolithic microwave IC (MMIC) having the field effect transistor (FET), the capacitor, etc. has been known.
As the steps of manufacturing such compound semiconductor device, for example, the FET having a gate electrode whose gate length is less than 1 xcexcm is formed, then the capacitor is formed, and then all of the FET and the capacitor are covered with the insulating protective film having good coverage.
A configuration of such capacitor will be explained with reference to FIG.1 hereunder.
In FIG.1, an underlying insulating film 102 is formed on a semiconductor substrate 101 such as GaAs, and a lower electrode 104, a dielectric film 105, and an upper electrode 106 constituting the capacitor 103 are formed in sequence on the underlying insulating film 102. The capacitor is covered with an insulating protective film 107. The lower electrode 104 and the upper electrode 106 come into contact with the insulating protective film 107.
Since the insulating protective film 107 is formed to cover the FET (not shown) together with the capacitor 103, good coverage and low stress are requested for such insulating protective film 107. A weak stress film can be obtained by forming a low density film to be thin such as about 40 to 60 nm.
However, according to the inventor""s experiment, it becomes apparent that a leakage current flows from the upper electrode to the lower electrode via the insulating protective film 107 in the capacitor.
As such insulating protective film, for example, the silicon nitride film which is formed by the ultraviolet (UV)-CVD method is employed. The hydrogen containing rate in the low density silicon nitride film is in excess of 30%. The silicon nitride film is grown at the substrate temperature of 200 to 400xc2x0 C.
If the silicon nitride film is formed at the substrate temperature of more than 600xc2x0 C., the high density film can be obtained because the hydrogen containing rate is reduced lower than 30%. However, if the substrate temperature is increased up to 600 xc2x0 C., silicon serving as the impurity doped in the compound semiconductor substrate 101 is activated and moved therein. Therefore, such an undesired phenomenon peculiar to the compound semiconductor device is caused that crystal defect is produced in the compound semiconductor substrate.
If the film thickness of the insulating protective film 107 is formed thicker than 60 nm, there is such a disadvantage that the piezo effect is generated in the compound semiconductor substrate around the gate electrode of the FET, due to the stress by the insulating protective film 107, to thus generate a parasitic capacitance.
It is an object of the present invention to provide a compound semiconductor device having a structure which is capable of reducing a leakage current flowing between an upper electrode and a lower electrode of a capacitor via an insulating protective film and a method of manufacturing the same.
The above subject can be overcome by providing a compound semiconductor device comprising a first electrode of a capacitor, formed on a compound semiconductor substrate via a first insulating film; a dielectric film of the capacitor, formed on the first electrode; a second electrode of a capacitor, formed on the dielectric film; a second insulating film for covering an upper surface and side surfaces of the second electrode; and an insulating protective film for covering the second insulating film, the dielectric film, the first electrode and the first insulating film, and having a hydrogen containing rate which is larger than the second insulating film.
According to the present invention, in the capacitor including the first electrode, the dielectric film, and the second electrode, the first electrode is selectively covered with the insulating film which has the low hydrogen containing rate, and also all the capacitor including the insulating film and the substrate are covered with the insulating protective film which has good coverage and has the high hydrogen containing rate.
Therefore, direct contact between the first electrode and the second electrode can be avoided by the insulating protective film, so that the leakage current can be prevented from flowing between the first electrode and the second electrode via the insulating protective film.
If the plasma CVD method is employed as the growth method of the second insulating film in the event that the second insulating film for covering selectively the second electrode is formed of the silicon nitride or the silicon nitride oxide (SiOxNy (x, y are component number)), the second insulating film can be formed at the substrate temperature of less than 400xc2x0 C. Therefore, movement of the impurity is hard to cause in the compound semiconductor substrate below the second insulating film, so that generation of the crystal defect in the compound semiconductor substrate can be prevented.